Hyporheic Exchange in the Petit Buëch, Southern France
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A point bar along the Petit Buëch in southern France was studied for the effect of the interaction between groundwater and surface water. This so-called hyporheic exchange was clearly visible at multiple locations on the point bar. Residence time increases when water from the river infiltrates into the subsurface, influencing the transportation of nutrients and pollutants. A fieldwork was performed to do measurements on elevation, porosity and hydraulic conductivity. Grain size measurements were performed to calculate a porosity of 0.18 to 0.35. Hydraulic conductivity was calculated using porosity and groundwater velocity, resulting in an average hydraulic conductivity of 0.16 m/s. In ArcGIS the measurements were interpolated. Interpolations showed locations of large hydraulic conductivity in the inland part of the study area. In groundwater flow model MODFLOW, random fields of hydraulic conductivity were imported for particle tracing experiments in PMPATH. These resulted in residence time distributions having an average residence time of ~20 days. Fluxes were calculated along the river boundary, indicating a surplus of water infiltrating into the area of 1.6 m/s. Either the water exfiltrates into gullies on the point bar or elsewhere beyond the study area.